In typical plug and perforate systems the bottom hole assembly (BHA) comprises an isolation device with a passage through it and a surrounding seat on the passage for an object to land on the seat and obstruct the passage. The object can be delivered with the isolation device or pumped to the isolation device after the perforating guns are shot and removed from the borehole with the setting tool for the isolation device. Delivering the object with the isolation device has the advantage of saving time to get the passage in the isolation device closed as compared to pumping down an object from the surface. However, this prior method has a drawback if the guns misfire. In essence, if the guns misfire they must be removed and new guns run in to the desired location which is frequently in a horizontal portion of the wellbore. Thus, gravity is not much help in running in the replacement guns. Furthermore, if the object was run in with the isolation device, then the object would be forced against the seat in the passage of the isolation device if any effort to use pressure or flow to deliver the replacement guns was employed. The closing off of the passage in the isolation device means the replacement guns cannot be delivered on wireline with a pressure or flow assist and that alternative means such as coiled tubing or tractors have to be used to get the guns into position. This adds enormous expense to the operation and creates issues of delay. Even if the object is dropped after the misfired gun is removed, it still takes time to pump the object from the surface to the seat on the isolation device that is thousands of meters away costing time and additional fluid displacement.
In the past one way to cut the time to get an object seated on a seat in an isolation device was to include a ball release device above the guns. The idea in US 2013/0175053 was to release the object into the annulus from above the fired gun and have the object make its way around the fired gun and the isolation device setting tool to a seat on a passage in the isolation device. A physical pull on the wireline sheared an unnumbered pin and allowed a ball 24 to escape through a lateral opening 28 to make its way toward the isolation device 14. There are many issues with this design. Frequently the guns 18 have very low clearance around them to the casing 12, which means the ball 24 will not fit in the annular space or would have to be so small that the passage in the isolation device 14 would also have to be small. A smaller passage in the isolation device could mean delays if a replacement gun has to be delivered with flow after an original gun misfires. The spent perforating gun could also have burrs and sharp edges that could hang up or damage the object so badly that it might not seal at all when landing in the seat. Finally, in a horizontal run the object may not actually land on the seat if the seat surrounding the passage in the isolation device is considerably smaller than the casing inside diameter, a condition made necessary by the object being small enough to travel past the gun in the surrounding annulus around the gun.
Generally related to operation of lateral passages that can be selectively opened in a fracking context are US2013/0024030 and US2013/0020065.
What is needed is a device and method that allows retention of the object that is designed to go onto a seat for a passage in an isolation until such time as the gun actually fires. The reason is that if the guns misfire and need to be replaced, it will still be possible to deliver the replacement guns with pressure or flow because the passage in the isolation device will be open because the object has been retrieved with the misfired guns. What is also provided is a launcher for the object that is placed in close proximity of the isolation device which allows the use of a larger object than when the launcher is above the guns and has to deliver the object into an annulus between the gun and the casing after the gun fires. What is also provided is an object launching device that responds directly or indirectly to the concussive pressure shock created by the guns initially firing so that the object is only released if the guns actually fire. This allows for the object to be retrieved without release if the guns misfire so that the replacement guns can be delivered with flow through the still open passage in the isolation device. On the other hand, if the guns fire then the pressure that is built up from the firing will release the object allowing the start of fracturing after the guns and setting tool for the isolation device are pulled out. Those skilled in the art will further appreciate additional aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.